Phylum Arthropoda“jointed appendaged animals’

• The phylum with the greatest number of species

• Four lineages:– Trilobites (all extinct)

– Chelicerates (spiders, mites, scorpions)

– Crustaceans (crabs, shrimps, barnacles)

– Uniramians (insects, centipedes, millipedes)

Arthropods: Phylum Arthropoda

Adaptations for Success

• Hardened exoskeleton

• Jointed appendages

• Fused and modified segments

• Respiratory structures

• Specialized sensory structures

• Division of labor

Do not post on Internet

Figure 25.26Page 432

• Originated in seas

• A few are still marine: horseshoe crabs, sea spiders

• The arachnids are all terrestrial

Spiders Mites

Scorpions Chiggers

“Daddy longlegs” Ticks

Chelicerates

Subphylum Chelicerata

These are the scorpions, spiders, mites, horseshoe crabs, and "sea spiders." Chelicerates have six pairs of appendages, which are uniramous (unbranched). These include a pair of chelicerae, a pair of pedipalps, and four pairs of walking legs. Chelicerates lack mandibles and antennae. Respiration is by means of book gills, book lungs, or tracheae.

Class Arachnida

Arachnids have a pair of tagmata called a prosoma (cephalothorax) and opisthosoma (abdomen). The prosoma is partially or completely covered with a carapace-like shield. The opisthosoma may be segmented or unsegmented. The appendages on the opithosoma are absent or modified, being used as spinnerets (spiders) or pectines (probably sensory in function, found in scorpions). Respiration is via tracheae or book lungs; it is cutaneous in many small arachnids.

house spiderAchaearanea tepidariorum

Body Plan of a Spider

eye

poison gland

chelicera

mouth

book lung

sperm receptacle

ovary silk gland

spinners

anus

Malpighian tubuledigestive glandheartbrain

pedipalp

Figure 25.28Page 433

beach wolf spiderArctosa littoralis

• Most are marine, some freshwater, a few terrestrial

• Head has two pairs of

antenna, three pairs

of food-handling

appendages

Crustaceans

Copepods

Crayfish

Barnacles

Lobsters

Shrimps

Crabs

Isopods (pillbugs)

Lobster Body Plan

antennae (two pairs)

one of two eyes

fused segments of cephalothorax

segments of abdomen

tail fin

swimmerets

five walking legs (five pairs total)

first leg

food-handling appendages (three pairs)

Figure 25.29aPage 434

Subphylum Crustacea(crustaceans)

Members of the Subphylum include lobsters, crabs, crayfish, shrimp, copepods, barnacles, and several other groups of organisms. All have two pairs of antennae, a pair of mandibles, a pair of compound eyes (usually on stalks), and two pair of maxillae on their heads, followed by a pair of appendages on each body segment (crustacean bodies usually are made up of head, thorax, and abdomen, although the segments composing these tagmata differ among different Classes). The appendages are primitively branched (biramous), and although this condition is modified in many species, adults always have at least some biramous appendages. Crustaceans respire via gills. Like other arthropods, all have a hard but flexible exoskeleton.

blue crabCallinectes sapidus

Daphnia pulex

rusty crayfishOrconectes rusticus

yellowline arrow crabStenorhynchus seticornis

Uniramia

Uniramians are arthropods whose appendages are unbranched. Most appendages are made up of several articulating pieces. The uniramian body has two or three tagmata, and the abdomen contains numerous segments. The head appendages include paired antennae and mandibles, and also two pairs of maxillae (the second pair may be fused or sometimes absent). "Breathing" is by means of tracheae and spiracles. The sexes are separate, but most other aspects of reproduction are extremely varied.

Class Insecta(insects)

A number of features, however, are shared by most kinds of living insects. In addition to the general characteristics of uniramians, these include a body composed of three tagmata, a head, thorax, and abodmen; a pair of relatively large compound eyes and usually three ocelli located on the head; a pair of antennae, also on the head; mouthparts consisting of a labrum, a pair of mandibles, a pair of maxillae, a labium, and a tonguelike hypopharynx; two pairs of wings, derived from outgrowths of the body wall (unlike any vertebrate wings); and three pairs of walking legs.

Insect Body Plan

• Thorax usually has three pairs of legs and one or two pairs of wings

• Abdomen contains most internal organs and specialized structure for reproduction

• Three-part gut

• Malpighian tubules attach to midgut and

serve in elimination of wastes

Insect Diversity

• The only winged invertebrates

• More than 800,000 known species

• Most successful species are small in size and have a great reproductive capacity

yellow fever mosquitoAedes aegypti

black-and-yellow argiopeArgiope aurantia redlegged grasshopperMelanoplus femurrubrum

band-winged grasshoppersOedipodinae

Class Chilopoda(centipedes)

Centipedes are uniramian arthropods whose bodies are made up of a chain of many (up to 177) flattened segments, each except the one behind the head and last two bearing a single pair of appendages (legs). The appendages of the first body segment have been modified to form large, poisonous fangs that are used to capture prey. The bite of a large centipede, however, can be painful to an adult and dangerous to a small child.

Millipedes and Centipedes

• Segmented bodies with many legs• Millipedes

– Two pairs of legs per “segment”– Scavengers

• Centipedes– Flattened, with one pair of legs per

segment– Predators

Class Diplopoda(millipedes)

Like centipedes, millipedes have bodies that are made up of numerous segments. The first four thoracic segments each bear a single pair of legs, but the following abdominal segments all have two pairs. Millipedes lack poisonous fangs and do not bite; rather, to discourage predators they roll into a defensive ball and many emit poisonous or foul-smelling substances.

Narceus americanus